This invention relates to improvements in a catalytic converter having a monolithic catalyst carrier so as to purify exhaust gas from an internal combustion engine, and more particularly to improvements in a catalyst carrier supporting device having an elastic washer to be used to axially elastically support the monolithic catalyst carrier in a casing of the catalytic converter.
Most automotive vehicles are equipped with a catalytic converter for the purpose of purifying exhaust gas discharged from an internal combustion engine. For example, the catalytic converter is constructed such that a monolithic catalyst carrier is encased within a casing including a part of an exhaust manifold. The monolithic catalyst carrier formed of ceramic is brittle and tends to be readily damaged, and therefore it is required to be elastically supported within the casing. Specifically, as disclosed in Japanese Patent Provisional Publication No. 7-317537, a cylindrical supporting member formed of a corrugated cylindrical wire mesh structure is disposed around the monolithic catalyst carrier so as to radially elastically support the monolithic catalyst carrier. Additionally, annular elastic washers formed of an annular wire mesh structure are disposed respectively in press contact with the outer peripheral portions of the opposite end faces of the monolithic catalyst carrier so as to axially elastically support the monolithic catalyst carrier.
Each elastic washer is produced by first weaving an annular structure of wire mesh so as to possess a suitable rigidity and then by forcing the wire mesh annular structure into a mold having a certain shape so that the wire mesh annular structure has a rectangular cross-section. The thus produced elastic washer is located in the casing such that a part of the elastic washer projects radially outward of the outer peripheral surface of the monolithic catalyst carrier. In other words, the elastic washer is located to extend radially inward and outward of the outer peripheral surface of the monolithic catalyst carrier. In an assembled state of the catalytic converter in which the casing is tightly closed with bolts or the like, the elastic washer is in a condition to be compressed by a certain amount. Additionally, the elastic washer is usually supported by an annular metal member having an inner peripheral wall to be located along the inner peripheral surface of the elastic washer. For example, in an arrangement disclosed in the above-mentioned Japanese Patent Provisional Publication, an annular metallic carrier supporting plate is provided to retain the elastic washer in a manner to cause the elastic washer to be in press contact with an end face of the monolithic catalyst. Additionally, the elastic washer is positioned between an annular inner peripheral wall of the carrier supporting plate and an inner peripheral portion of the casing.
Besides, the following structure has been put into practical use: The above-mentioned metallic carrier supporting plate is replaced with an annular cap including annular inner and outer peripheral walls and an annular bottom wall so as to have a generally U-shaped cross-section. Thus, this annular cap is formed with an annular groove in which the annular elastic washer is fitted to be retained there.
Under the action of such carrier supporting plate and cap, the elastic washer is positioned at a certain location while being protected from oxidation with high temperature exhaust gas though the elastic washer is formed of the wire mesh.
In connection with the catalytic converter having the above-discussed structure which has been put into practical use, the monolithic catalyst carrier formed of ceramic has a plurality of cells extending from its upstream-side end face to its downstream-side end face. Each cell is defined by walls having a thickness of several mil ({fraction (1/1000)} inch). Accordingly, the walls of the cells tend to readily damaged, in which the wall located at the outer-most peripheral portion particularly tends to be readily peeled off by a slight external force.
During operation of the catalytic converter, the metallic carrier supporting plate with the elastic washer is repeatedly radially displaced upon repetition of thermal expansion and contraction although the monolithic catalyst carrier hardly makes its thermal expansion and contraction. Consequently, the elastic washer is radially outwardly displaced upon thermal expansion of the carrier supporting plate under operation of the engine, thereby radially outwardly pulling the outer peripheral portion of the monolithic catalyst carrier at the end face. This causes the outer peripheral portion at the end face of the monolithic catalyst to be peeled off.
Thus, the outer peripheral portion of the monolithic catalyst carrier at the end face tends to be readily peeled off and damaged. If the outer peripheral portion is once broken off, an axial free movement of the monolithic catalyst carrier becomes large, and therefore total damage of the monolithic catalyst carrier abruptly progresses under vibration or the like during vehicle cruising.
It is, therefore, an object of the present invention to provide an improved catalytic converter which can effectively overcome drawbacks encountered in conventional catalytic converters.
Another object of the present invention is to provide an improved catalytic converter in which a monolithic catalyst carrier in a casing can be effectively protected from being damaged in its outer peripheral portion at an end face.
A further object of the present invention is to provide an improved catalytic converter in which an outer peripheral portion of a monolithic catalyst carrier at the end face can be effectively prevented from being radially outwardly pulled by an elastic washer which is in press contact with the outer peripheral portion of the monolithic catalyst carrier.
A still further object of the present invention is to provide an improved catalytic converter in which an elastic washer retained by a metallic cap can be prevented from being radially outwardly displaced even upon radially outward displacement of the cap owing to thermal expansion of the cap.
A catalytic converter according to the present invention comprises a casing. A monolithic catalyst carrier is disposed inside the casing. An annular cap is fixedly disposed inside the casing and located generally coaxial with the monolithic catalyst carrier. The annular cap is located near an end face of the monolithic catalyst carrier. The cap includes annular bottom, inner and outer walls. The inner and outer walls are separate from each other and extend from the bottom wall. The inner wall is located radially inward of the outer wall. The bottom, inner and outer walls are arranged generally U-shaped in cross-section so as to form a groove. Additionally, an annular elastic washer is coaxially disposed within the groove of the annular cap. The elastic washer is disposed in press contact with the end face of the monolithic catalyst carrier to axially elastically support the monolithic catalyst carrier. The annular elastic washer is an annular molded structure of wire mesh. The annular elastic washer has an inner peripheral face which has a diameter larger than a diameter of an outer peripheral surface of the inner wall of the cap so as to form a clearance between the elastic washer and the inner wall of the cap in a state where the elastic washer is assembled in the casing upon being compressed.